System and method for reducing corrosion in a compressor

ABSTRACT

A system for reducing corrosion in a compressor includes a compressor blade having a corrosion potential. A sensor connected to the compressor blade generates a signal reflective of the corrosion potential. A power supply connected to the compressor blade at an electrical connection produces an electrical potential at the electrical connection. An electrolyte coats at least a portion of the sensor and the electrical connection. A method for reducing corrosion in a compressor includes sensing a corrosion potential of a compressor blade and generating a signal reflective of the corrosion potential. The method further includes generating an electrical potential at an electrical connection on the compressor blade and flowing an electrolyte over at least a portion of the compressor blade and the electrical connection.

FIELD OF THE INVENTION

The present invention generally involves a system and method forreducing and/or preventing corrosion in a compressor. Particularembodiments of the present invention may employ anodic protection,cathodic protection, and/or impressed current techniques to reduceand/or prevent general corrosion of compressor blades.

BACKGROUND OF THE INVENTION

A typical compressor includes multiple stages of rotating and fixedblades made from various steel alloys. Ambient air flows into thecompressor, and the rotating blades progressively impart kinetic energyto the ambient air to produce a compressed working fluid at a highlyenergized state. The ambient air often includes various amounts ofmoisture, salts, acids, and other pollution and contaminants that maydeposit or precipitate onto the rotating and fixed blades. The build upof pollution and contaminants on the blade surfaces results in anenvironment conducive to increased levels of general, crevice, and/orpitting corrosion on the compressor blades.

Various methods are known in the art for reducing and/or preventingcorrosion of steel alloys. For example, a passive oxide film or layermay be formed on the surface of the steel alloy to inhibit generalcorrosion and the onset of crevice and/or pitting corrosion. Apolarization plot or curve may be created to correlate the corrosionpotential (E_(corr)) and current density (I) across the surface of thepassivated steel alloy to the onset of particular forms of corrosion.For example, as shown in FIG. 1, the passive oxide film may protect thesurface of the steel alloy by reducing the increase in the currentdensity (I), and thus the general corrosion rate, as the corrosionpotential (E_(corr)) increases across the surface of the steel alloy.Eventually, the corrosion potential (E_(corr)) reaches the pittingbreakdown potential (E_(b)), at which point the current density (I)increases dramatically, resulting in pitting corrosion, crevicecorrosion, and/or other forms of localized corrosion on the surface ofthe steel alloy. The localized corrosion may continue to occur until thecorrosion potential (E_(corr)) decreases below the repassivationpotential (E_(rp)).

Anodic and cathodic protection systems have been successfully used tocontrol or adjust the corrosion potential (E_(corr)), and thus theamount and type of corrosion, in many industrial applications. However,anodic and cathodic protection systems generally require an electricallyconductive path surrounding or connected to the component beingprotected. For example, soil around a pipeline, liquid in a tank, andseawater around marine structures and ships provide the electricallyconductive path that enables anodic and cathodic protection systems towork in those environments. However, the structure and environment of acompressor generally lacks a similar conductive path suitable for anodicand cathodic protection systems. Specifically, the ambient air flowingacross the rotating and fixed blades does not produce sufficientelectrical conductivity to support an anodic or cathodic protectionsystem. Therefore, an improved system and method that provides anodicand/or cathodic protection to compressors would be useful.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention are set forth below in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

One embodiment of the present invention is a system for reducingcorrosion in a compressor. The system includes a compressor blade havinga corrosion potential. A sensor is connected to the compressor blade,and the sensor generates a signal reflective of the corrosion potentialof the compressor blade. A power supply is connected to the compressorblade at an electrical connection, and the power supply produces anelectrical potential at the electrical connection. An electrolyte coatsat least a portion of the sensor and the electrical connection.

Another embodiment of the present invention is a system for reducingcorrosion in a compressor that includes a compressor blade having acorrosion potential and a sacrificial anode connected to at least aportion of the compressor blade. An electrolyte coats at least a portionof the compressor blade and the sacrificial anode.

The present invention may also include a method for reducing corrosionin a compressor. The method includes sensing a corrosion potential of acompressor blade and generating a signal reflective of the corrosionpotential of the compressor blade. The method further includesgenerating an electrical potential at an electrical connection on thecompressor blade and flowing an electrolyte over at least a portion ofthe compressor blade and the electrical connection.

Those of ordinary skill in the art will better appreciate the featuresand aspects of such embodiments, and others, upon review of thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is an exemplary polarization graph;

FIG. 2 is a simplified diagram of a system according to one embodimentof the present invention;

FIG. 3 is a simplified diagram of a system according to a secondembodiment of the present invention;

FIG. 4 is a simplified diagram of a system according to a thirdembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to present embodiments of theinvention, one or more examples of which are illustrated in theaccompanying drawings. The detailed description uses numerical andletter designations to refer to features in the drawings. Like orsimilar designations in the drawings and description have been used torefer to like or similar parts of the invention.

Each example is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that modifications and variations can be made in thepresent invention without departing from the scope or spirit thereof.For instance, features illustrated or described as part of oneembodiment may be used on another embodiment to yield a still furtherembodiment. Thus, it is intended that the present invention covers suchmodifications and variations as come within the scope of the appendedclaims and their equivalents.

Embodiments within the scope of the present invention provide a systemand method for reducing and/or preventing corrosion in a compressorusing anodic, cathodic, and/or impressed current techniques. In specificembodiments, an electrolyte may be supplied, flowed, or sprayed into thecompressor to provide an electrically conductive medium that enablesanodic and/or cathodic protection techniques to reduce or preventcorrosion on the compressor blades. In other specific embodiments, thecorrosion potential (E_(corr)) of the compressor blades may be sampled,and an electrical potential may be provided to specific areas or regionsof the compressor blades to increase or decrease the local corrosionpotential (E_(corr)) at that area or region, as desired.

FIG. 2 provides a simplified diagram of a system 10 according to oneembodiment of the present invention. In this particular embodiment, thesystem 10 provides anodic protection against corrosion and generallyincludes a sensor 12 and a power supply 14 connected to one or morecompressor blades 16. The system 10 further includes an electrolyte 18that coats or covers at least a portion of the compressor blades 16. Thecompressor blades 16 may be fixed or rotating blades. If the compressorblades 16 are fixed, the wiring for the sensor 12 and the power supply14 may pass through the inside of the compressor blades 16 and out ofthe stationary portion of the compressor. Alternately, if the compressorblades 16 are rotating blades, brushes and slip rings (not shown) may beused to provide electrical connectivity between the rotating blades andthe stationary sensor 12 and power supply 14, as is known in the art. Ineither event, the compressor blades 16 may include a nonconductive liner20 to electrically insulate the compressor blades 16 from any straycurrents that may affect the accuracy or sensitivity of the sensor 12.

The sensor 12 may comprise any instrument capable of detecting and/ormeasuring a voltage or current flow across at least a portion of thecompressor blade 16. For example, the sensor 12 may comprise a voltmeter22, an ammeter, and/or a conventional corrosion sensor 24 installed on asurface of the compressor blade 16. The corrosion sensor 24 may connectto the component surface 16 at a sensor connection 26 and also to areference electrode 28 in the electrolyte 18 to complete the electricalcircuit.

The corrosion sensor 24 and/or the voltmeter 22 may produce a signal 30reflective of a corrosion potential of the compressor blade 16. Thesignal 30 may comprise, for example, a current or voltage magnitudewhich may be proportional to the amount and/or rate of general corrosionoccurring on the compressor blade 16. The signal 30 may be manuallyinterpreted and acted on by an operator to adjust the power supply 14 asdesired. Alternately, or in addition, as shown in FIG. 2, the system 10may include a controller 32 configured or programmed to receive thesignal 30 and adjust the power supply 14. As described herein, thetechnical effect of the controller 32 is to adjust the power supply 14to achieve a desired voltage and/or current out of the power supply 14.The controller 32 may be a stand alone component, such as apotentiometer, or a sub-component included in any computer system knownin the art, such as a laptop, a personal computer, a mini computer, or amainframe computer. The various controller and computer systemsdiscussed herein are not limited to any particular hardware architectureor configuration. Embodiments of the systems and methods set forthherein may be implemented by one or more general-purpose or customizedcontrollers adapted in any suitable manner to provide the desiredfunctionality. For example, the controller 32 may be adapted to provideadditional functionality, either complementary or unrelated to thepresent subject matter. When software is used, any suitable programming,scripting, or other type of language or combinations of languages may beused to implement the teachings contained herein. However, some systemsand methods set forth and disclosed herein may also be implemented byhard-wired logic or other circuitry, including, but not limited to,application-specific circuits. Of course, various combinations ofcomputer-executed software and hard-wired logic or other circuitry maybe suitable as well.

The power supply 14 may comprise any variable source of direct currentand may connect to each compressor blade 16 at an electrical connection34 and also to a counter electrode 36 in the electrolyte 20 to completethe electrical circuit. For example, the power supply 14 may comprise abattery capable of providing 5 to 500 milliamps of current at voltagesless than 15 V DC. However, the size and capacity of the power supply 14will depend on the particular use, and the present invention is notlimited to any particular size or capacity of the power supply 14 unlessspecifically recited in the claims. As shown in FIG. 2, an ammeter 38may be used with the power supply 14 to measure and/or supply thedesired current and voltage to the component surface 16.

As shown in FIG. 2, the electrolyte 18 coats or covers at least aportion of the compressor blade 16, the sensor connection 26, and/or theelectrical connection 34. The electrolyte 18 may comprise any fluidcapable of conducting electron flow. For example, the electrolyte 18 maycomprise a solution of bicarbonate of soda, salt water, or other ionizedsolutions known to one of ordinary skill in the art. The electrolyte 18may be supplied, flowed, or sprayed into the compressor as thecompressor operates so that the electrolyte 18 flows over the compressorblades 16 and coats or covers at least a portion of the compressorblades 16, the sensor connection 26, and/or the electrical connection34. In this manner, the electrolyte 18 provides the conductive mediumthat enables electron flow between the power supply 14 and thecompressor blades 16.

During operation of the system 10, the sensor 12 detects and/or measuresthe corrosion potential across at least a portion of the compressorblades 16 and generates the signal 30 reflective of the corrosionpotential of the compressor blade 16. The controller 32, if present, oran operator may receive the signal 30 and adjust the power supply 14 toproduce a desired electrical potential at the electrical connection 34.The electrical potential produced at the electrical connection 34combines with the existing corrosion potential to result in a desiredcorrosion potential across the compressor blades 16. For example,referring to the exemplary polarization graph previously described withrespect to FIG. 1, the electrical potential produced across theelectrical connection 34 would ordinarily dampen or reduce the currentdensity (I) across the compressor blade 16, shifting the polarizationcurve to the left. The resulting lower current density (I) for a givencorrosion potential thus results in reduced general corrosion across thesurface of the compressor blade 16.

FIG. 3 provides a simplified diagram of a system 40 according to asecond embodiment of the present invention. In this particularembodiment, the system 40 provides cathodic protection against corrosionand generally includes the compressor blades 16 and electrolyte 18 aspreviously described with respect to the embodiment shown in FIG. 2. Inaddition, this embodiment includes a sacrificial anode 42 connected tothe compressor blades 16, and the electrolyte 18 coats or covers atleast a portion of the sacrificial anode 42 and compressor blades 16.

The sacrificial anode 42 may comprise any suitable material known in theart that has a higher oxidation potential or more negativeelectrochemical potential than the steel alloy used in the compressorblades 16. For example, the sacrificial anode 42 may comprise a plate,rod, or fin made from aluminum, zinc, or another element in the galvanicseries above martensitic steel. As the electrolyte 18 coats at least aportion of the compressor blades 16 and the sacrificial anode 42, thesacrificial anode 42 protects the compressor blades 16 from generalcorrosion by preferentially corroding before the steel alloy in thecompressor blades 16. Although the electrolyte 18 coating at least aportion of the sacrificial anode 42 and compressor blades 16 enables thesystem 40 shown in FIG. 3 to operate, the preferential corrosion of thesacrificial anode 42 may cause portions of the sacrificial anode 42 tobreak off during operation, resulting in undesirable debris flowingthrough the compressor. This obvious disadvantage may be monitored andminimized through regular inspection and maintenance intervals thatcheck the condition and/or replace the sacrificial anode 42 asnecessary.

FIG. 4 provides a simplified diagram of a system 50 according to a thirdembodiment of the present invention that incorporates or combinesaspects of the previous embodiments shown and described with respect toFIGS. 2 and 3 to provide impressed current cathodic protection againstcorrosion. Specifically, the system 50 includes a sensor 12 and a powersupply 14 connected to one or more compressor blades 16 as previouslydescribed with respect to the embodiment shown in FIG. 2. In addition,the system includes a sacrificial anode 42 as previously described withrespect to the embodiment shown in FIG. 3. Notably, the power supply 14may connect to the compressor blade 16 at an electrical connection 34 onthe sacrificial anode 42 and also to a counter electrode 36 in theelectrolyte 18 to complete the electrical circuit. As a result, theelectrical potential or impressed current provided by the power supply14 increases the difference in the electrochemical potential between thesacrificial anode 42 and the compressor blades 16.

During operation of the system 50, the sacrificial anode 42 protects thecompressor blades 16 from general corrosion by preferentially corrodingbefore the steel alloy in the compressor blades 16, as previouslydescribed with respect to the embodiment shown in FIG. 3. In addition,in the event that the sacrificial anode 42 is unable to provide completeprotection to the compressor blade 16, the sensor 12 detects and/ormeasures the corrosion potential across at least a portion of thecompressor blades 16 and generates the signal 30 reflective of thecorrosion potential of the compressor blade 16. The controller 32, ifpresent, or an operator may receive the signal 30 and adjust the powersupply 14 to produce a desired electrical potential at the electricalconnection 34. As a result, the electrical potential produced at theelectrical connection 34 increases the difference in the electrochemicalpotential between the sacrificial anode and the compressor blades 16 toenhance the cathodic protection to the compressor blades 16.

The systems 10, 40, 50 described and illustrated in FIGS. 2-4 may alsoprovide a method for reducing corrosion in the compressor. The methodmay generally include sensing the corrosion potential of the compressorblade 16 and generating the signal 30 reflective of the corrosionpotential. The method may further include generating the electricalpotential at the electrical connection 34 on the compressor blade 16 andflowing the electrolyte 18 over at least a portion of the compressorblade 16 and the electrical connection 34. Particular embodiments of themethod may further include connecting the sacrificial anode 42 to atleast a portion of the compressor blade 16 and/or connecting theelectrical connection 34 to the sacrificial anode 42.

One of ordinary skill in the art will readily appreciate that thesystems and methods previously described enhance the ability to monitorand/or control the corrosion potential in the compressor related 16 toreduce corrosion in the compressor. By reducing the corrosion in thecompressor, the compressor may be operated for longer periods betweeninspections and maintenance, and unplanned outages to repair or replacecorroded compressor blades may be reduced or eliminated altogether.Alternately, or in addition, the reduced corrosion in the compressor mayallow for lower-cost steel alloys to be incorporated into the compressorblades to reduce the initial capital cost of the compressor. Finally,the addition of the electrolyte 18 into the compressor may enhancecleaning of corrosive contaminants from the compressor blades 16 and/ormore frequent increased power augmentation provided by the injectedelectrolyte 18.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other and examples areintended to be within the scope of the claims if they include structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal languages of the claims.

1. A system for reducing corrosion in a compressor comprising: a. acompressor blade, wherein the compressor blade has a corrosionpotential; b. a sensor connected to the compressor blade, wherein thesensor generates a signal reflective of the corrosion potential of thecompressor blade; c. a power supply connected to the compressor blade atan electrical connection, wherein the power supply produces anelectrical potential at the electrical connection; and d. anelectrolyte, wherein the electrolyte coats at least a portion of thesensor and the electrical connection.
 2. The system as in claim 1,further comprising a controller that receives the signal reflective ofthe corrosion potential of the compressor blade from the sensor.
 3. Thesystem as in claim 1, further comprising a controller that adjusts theelectrical potential at the electrical connection based on the signalfrom the sensor.
 4. The system as in claim 1, further comprising asacrificial anode connected to at least a portion of the compressorblade.
 5. The system as in claim 4, wherein the electrolyte coats atleast a portion of the sacrificial anode.
 6. The system as in claim 4,wherein the electrical connection is connected to the sacrificial anode.7. A system for reducing corrosion in a compressor comprising: a. acompressor blade, wherein the compressor blade has a corrosionpotential; b. a sacrificial anode connected to at least a portion of thecompressor blade; and c. an electrolyte, wherein the electrolyte coatsat least a portion of the compressor blade and the sacrificial anode. 8.The system as in claim 7, further comprising a sensor connected to thecompressor blade, wherein the sensor generates a signal reflective ofthe corrosion potential of the compressor blade.
 9. The system as inclaim 8, further comprising a power supply connected to the compressorblade at an electrical connection, wherein the power supply produces anelectrical potential at the electrical connection.
 10. The system as inclaim 9, wherein the electrolyte coats at least a portion of theelectrical connection.
 11. The system as in claim 9, further comprisinga controller that receives the signal reflective of the corrosionpotential of the compressor blade from the sensor.
 12. The system as inclaim 9, further comprising a controller that adjusts the electricalpotential at the electrical connection based on the signal from thesensor.
 13. The system as in claim 9, wherein the electrical connectionis connected to the sacrificial anode.
 14. A method for reducingcorrosion in a compressor comprising: a. sensing a corrosion potentialof a compressor blade; b. generating a signal reflective of thecorrosion potential of the compressor blade; c. generating an electricalpotential at an electrical connection on the compressor blade; and d.flowing an electrolyte over at least a portion of the compressor bladeand the electrical connection.
 15. The method as in claim 14, furthercomprising connecting a power supply to the electrical connection on thecompressor blade.
 16. The method as in claim 14, further comprisingadjusting the electrical potential at the electrical connection on thecompressor blade based on the signal reflective of the corrosionpotential of the compressor blade.
 17. The method as in claim 14,further comprising connecting a sacrificial anode to at least a portionof the compressor blade.
 18. The method as in claim 17, furthercomprising flowing the electrolyte over at least a portion of thesacrificial anode.
 19. The method as in claim 17, further comprisingconnecting the electrical connection to the sacrificial anode.